Gas generating composition

ABSTRACT

The present invention provides a gas generating composition including a fuel and an oxidizing agent, the fuel being melamine having a particle size (D 50 ), measured by a laser scattering method, of 35 μm or less.

This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2006-298663 filed in Japan on 2 Nov. 2006, which is incorporated by reference.

BACKGROUND OF INVENTION

1. Field of Invention

The present invention relates to a gas generating composition which can be used for an airbag restraining system for an automobile or the like.

2. Description of Related Art

Gas generating compositions for use in airbag restraining systems for automobiles or the like are required to generate gas including a low content of nitrogen oxide and carbon monoxide or the like and a small amount of mist, and also they are required to be capable of reducing the combustion temperature. Please see JP-A No. 2001-220282, JP-A No. 2004-67424, JP-A No. 11-343192 and JP-A No. 2006-76849.

Among the conventional arts, the gas generating compositions disclosed in the inventions of JP-A No. 2001-220282 and JP-A No. 2004-67424 excel in a low content of nitrogen oxide and carbon monoxide in generated gas, a reduced combustion temperature, and ability to reduce the amount of coolant/filter for cooling.

SUMMARY OF INVENTION

The present invention provides a gas generating composition including a fuel and an oxidizing agent, the fuel being melamine having a particle size (D₅₀), measured by a laser scattering method, of 35 μm or less.

DETAILED DESCRIPTION OF INVENTION

In terms of ignition ability in a state with a low ambient temperature, as in a winter season, the gas generating compositions disclosed in the inventions of JP-A No. 2001-220282 and JP-A No. 2004-67424 still have space for improvement.

The present invention relates to a gas generating composition that demonstrates good ignition ability within a wide temperature range from low temperatures to high temperatures, has a low combustion temperature, and generates gas including a low content of nitrogen oxide and carbon monoxide.

Further, the present invention provides the gas generating composition, further including guanidine nitrate as the fuel;

the gas generating composition, including basic or less. The fine-powder of melamine having such particle size demonstrates good ignition ability in a temperature range from a low temperature (for example, −40° C.) to a high temperature (for example, 80° C.), in spite of a low combustion temperature.

The gas generating composition in accordance with the present invention may use only fine powder of melamine as the fuel, but other known nitrogen-containing compounds may be used together with the aforementioned fine powder of melamine. When the fine powder of melamine is used together with other known nitrogen-containing compound, the content ratio of the fine powder of melamine is preferably 1 mass % or more, more preferably 3 mass % or more.

Examples of other known nitrogen-containing compounds may include one or two or more selected from tetrazole compounds such as 5-aminotetrazole, bitetrazole ammonium salt, guanidine compounds such as nitroguanidine, guanidine nitrate, and dicyandiamide, and triazine compounds such as trimethylol melamine, an alkylated methylol melamine, ammeline, ammelande, melamine nitrate, melamine peroxide, trihydrazinotriazine, and melamine nitro compounds. Among them, guanidine compounds such as nitroguanidine, guanidine nitrate, and dicyandiamide are preferred. Guanidine nitrate is especially preferable because, by combining this with the aforementioned melamine, an excessive drop in the combustion temperature of the gas generating composition can be inhibited and the combustion temperature can be adjusted to a desired range.

The content ratio of the aforementioned fine powder of melamine and guanidine nitrate when they are used together is preferably 10 to 1500 parts by mass, more preferably 25 to 1000 parts by mass, and even more preferably 50 to 750 parts by mass of guanidine nitrate per 100 parts by mass of the fine powder of melamine.

The content ratio of the fuel in the gas generating composition in accordance with the present invention is preferably 5 to 50 mass %, more preferably 7.5 to 45 mass %, and even more preferably 10 to 40 mass %.

The gas generating composition in accordance with the present invention preferably includes at least one of basic copper nitrate and basic copper carbonate as an oxidizing agent, but, if necessary, known oxidizing agents may be used together therewith. The basic copper nitrate and basic copper carbonate can be used individually, but it is preferred that the basic copper nitrate and basic copper carbonate be used together because the combustion temperature of the gas generating composition can be reduced and the amount of nitrogen oxide and carbon monoxide in the generated gas can be also reduced.

When the basic copper nitrate and basic copper carbonate are used together, it is preferred that the content ratio of basic copper carbonate be reduced, so that the content of basic copper carbonate be 1 to 80 parts by mass, preferably 2.5 to 60 parts by mass, even more preferably 5 to 50 parts by mass per 100 parts by mass of basic copper nitrate.

Examples of other oxidizing agents may include metal nitrates, ammonium nitrate, metal perchlorates, ammonium perchlorate, metal nitrites, metal chlorates, basic cobalt nitrate, basic zinc nitrate, and basic manganese nitrate.

The content ratio of the oxidizing agent in the gas generating composition in accordance with the present invention is preferably 40 to 95 mass %, more preferably 45 to 90 mass %, and even more preferably 50 to 85 mass %.

The gas generating composition in accordance with the present invention can further contain aluminum hydroxide. Adding aluminum hydroxide is preferred because the amount of nitrogen oxide and carbon monoxide in the generated gas can be reduced.

The content ratio of aluminum hydroxide in the gas generating composition in accordance with the present invention is preferably 0.1 to 20 mass %, more preferably 0.2 to 15 masse, and even more preferably 1 to 10 mass %.

The gas generating composition in accordance with the present invention can further contain a binder. Examples of the binder may include carboxymethyl cellulose, carboxymethyl cellulose sodium salt, carboxymethyl cellulose potassium salt, carboxymethyl cellulose ammonium salt, cellulose acetate, cellulose acetate butyrate, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl ethyl cellulose, microcrystalline cellulose, polyacrylamide, polyacrylamide amino compound, polyacrylhydrazine, copolymers of acrylamide and acrylic acid metal salt, copolymers of polyacrylamide and polyacrylic acid ester compound, polyvinyl alcohol, acrylic rubbers, guar gum, starch, and silicones.

The content ratio of the binder in the gas generating composition in accordance with the present invention is preferably 0.5 to 30 mass %, more preferably 1 to 20 mass %, and even more preferably 2 to 10 mass %.

If necessary, the gas generating composition in accordance with the present invention can also contain known additives that can be compounded with the gas generating compositions. Examples of known additives may include metal oxides such as copper oxide, iron oxide, zinc oxide, cobalt oxide, manganese oxide, molybdenum oxide, nickel oxide, bismuth oxide, silica, and alumina; metal hydroxides (however, excluding aluminum hydroxide) such as cobalt hydroxide, iron hydroxide, and magnesium hydroxide; metal carbonates or basic metal carbonates such as cobalt carbonate, calcium carbonate, basic zinc carbonate, and basic copper carbonate; complex compounds of a metal oxide or a metal hydroxide, such as Japanese acidic clay, kaolin, talc, bentonite, diatomaceous earth, and hydrotalcite; metallic acid salts such as sodium silicate, mica molybdate, cobalt molybdate, and ammonium molybdate; silicones, molybdenum disulfide, calcium stearate, silicon nitride, silicon carbide, boric acid, metaboric acid, and anhydrous boric acid.

The gas generating composition in accordance with the present invention can be molded into a desirable shape and can be obtained in the form of a cylindrical body with a single hole, a cylindrical body with multiple holes, and a pellet. These molded bodies can be manufactured by adding water or an organic solvent to the gas generating composition, mixing them and extrusion-molding (molded articles in the form of a cylinder with a single hole or a cylinder with multiple holes are obtained) or compression-molding by a pelletizer or the like (a molded article in the form of a pellet is obtained).

The gas generating composition in accordance with the present invention or a molded article obtained therefrom can be applied to an airbag inflator for a driver side, an airbag inflator for a passenger side, a side airbag inflator, an inflator for an inflatable curtain, an inflator for a knee bolster, an inflator for an inflatable seatbelt, an inflator for a tubular system, and a gas generator for a pretensioner in a variety of vehicles.

An inflator using the gas generating composition in accordance with the present invention or a molded article obtained therefrom may be of a pyrotechnic type in which gas is supplied only from a gas generating agent or of a hybrid type that gas is supplied from both a compressed gas such as argon and a gas generating agent.

Further, the gas generating composition in accordance with the present invention or a molded article obtained therefrom can be also used as an ignition agent called an enhancer agent (or a booster) that serves to transmit the energy of a detonator or squib to the gas generating agent.

EXAMPLES

The measurement methods are described below.

(1) Combustion Test

A gas generating agent that generates 0.9 mol of gas was sealed in a thick-wall chamber having an inner diameter of 75 mm and an internal height of 28 mm. An inner tube having a diameter of 20 mm was present in the central portion of the thick chamber, and 1.45 g of B/KNO₃ additive and an initiator were disposed inside the inner tube. Further, a plurality of nozzles having a diameter of 2 mm were provided in an open condition in the circumferential wall of the think-wall chamber. The pressure in the thick-wall chamber during combustion at an ambient temperature (23° C.) was adjusted to about 12 MPa by adjusting the number of the nozzles. The thick-wall chamber was placed into a low-temperature (−40° C.) atmosphere, an electric current was passed to the initiator, and the gas generating agent was ignited. The ignition state at this time was evaluated according to the following criteria.

Good: the gas generating agent was ignited within 10 ms after the initiator had been ignited.

Poor: the gas generating agent was not ignited even once 10 ms has elapsed after the initiator had been ignited.

(2) Combustion Temperature, Gas Output

Based on theoretical computations. The gas output represents the number of moles of the generated gas per 100 g of the composition (units: mol/100 g).

(3) Burning Rate

Powdered composition was filled into the mortar side of a predetermined die, and the composition was compressed and maintained for five seconds at a pressure of 14.7 MPa by a hydraulic pump from the end surface at the pestle side. The composition was then removed and molded to a cylindrical strand having an outer diameter of 9.6 mm and a length of 12.70 mm. The molded article was dried for sixteen hours at a temperature of 110° C., and then the strand density was calculated from the mass, diameter and height of the strand. Further, an epoxy resin adhesive of a chemical reaction type, Bond Quick 30, manufactured by KONISHI CO., LTD. was coated on the side surface and one end surface of the cylindrical molded article and cured for two hours or more at a room temperature to obtain a sample.

The cylindrical strand serving as a sample was disposed inside a sealed cylinder made from stainless steel SUS and having the internal capacity of 1 L, and the pressure inside the cylinder was raised and stabilized at 6.86 MPa, while purging the inside of the entire cylinder with nitrogen. A predetermined electric current was then passed to a nichrome wire that was brought in contact with the end surface of the strand, and the strand was ignited and combusted by the energy thereof. The behavior of pressure inside the cylinder with time was determined on a chart of a recorder, the time from the combustion start to the pressure rise peak was determined from the chart scale, and a numerical value obtained by dividing the strand length prior to combustion by the elapsed time was taken as a burning rate.

(4) Method for Measuring Gas Concentration

A cylindrical strand (mass: 2.00 g) prepared by the same method as in section (3) above was disposed inside a sealed cylinder made from stainless steel SUS and having the internal capacity of 1 L, and the pressure inside the cylinder was raised and stabilized at 7 MPa, while purging the inside of the entire cylinder with nitrogen. A predetermined electric current was then passed to a nichrome wire that was brought in contact with the end surface of the strand, and the strand was ignited and combusted by the melting or fusing energy thereof. After waiting for sixty seconds till the gas inside the cylinder became homogeneous, an open plug portion of a predetermined Teddler bag equipped with a plug was connected to the gas discharge portion of the cylinder, the combustion gas contained inside the cylinder was sampled by transferring into the bag, and NO₂, NO, NH₃, and CO concentrations were measured with gas detectors manufactured by GASTECH CORPORATION (No. 10 for NO₂ and NO detection; No. 3L for NH₃ detection, and No. 1L for CO detection).

The following is the components included in the used gas generating composition.

Fine powder of melamine: particle size (D₅₀), measured by a laser scattering method, of 35 μm or less.

Melamine: particle size (D₅₀), measured by a laser scattering method, of 35 μm to 50 μm.

GN: guanidine nitrate.

BCN: basic copper nitrate.

BCC: basic copper carbonate.

CMCNa: carboxymethyl cellulose sodium salt.

Embodiment 1, Comparative Example 1

The combustion test was performed with respect to the gas generating compositions including the components shown in Table 1. The results are shown in Table 1. TABLE 1 Gas generating composition −40° C. 23° C. 80° C. Example Fine powder of Good Good Good 1 melamine/BCN/ CMCNa/Al(OH)₃ = 16.32/73.68/5/5 Comparative Melamine/BCN/ Poor Poor Poor Example CMCNa/Al(OH)₃ = 1 16.32/73.68/5/5

Embodiment 2 to 4

Measurements were performed with respect to the gas generating compositions including the components shown in Table 2. The results are shown in Table 2. TABLE 2 Combustion Burning temperature Gas output rate Composition of generated gas Gas generating composition (° C.) (mol/100 g) (mm/sec) NO₂ NO NH₃ CO Example Fine powder of 1197 2.1346 14.88 0 140 55 175 2 melamine/BCN/CMCNa = 16.98/78.02/5 Example Fine powder of 1171 2.1576 14.21 0 100 65 240 3 melamine/BCN/CMCNa = 17.36/77.64/5 Example Fine powder of 1244 2.0907 13.99 0 200 37 165 4 melamine/BCN/CMCNa = 16.28/78.72/5

Embodiment 5 to 8

Measurements were performed with respect to the gas generating compositions including the components shown in Table 3. The results are shown in Table 3. TABLE 3 Combustion Burning temperature Gas output rate Composition of generated gas Gas generating composition (° C.) (mol/100 g) (mm/sec) NO₂ NO NH₃ CO Example Fine powder of 1085 2.1223 13.50 0 120 85 140 5 melamine/BCN/BCC/CMCNa = 16.82/73.12/5/5 Example Fine powder of 1052 2.0776 12.85 0 55 100 150 6 melamine/BCN/BCC/CMCNa = 16.29/68.71/10/5 Example Fine powder of 956 2.0289 11.57 0 18 65 170 7 melamine/BCN/BCC/CMCNa = 15.75/64.25/15/5 Example Fine powder of 857 1.9802 9.99 0 18 80 180 8 melamine/BCN/BCC/CMCNa = 15.21/59.79/20/5

Embodiment 9 to 12

Measurements were performed with respect to the gas generating compositions including the components shown in Table 4. The results are shown in Table 4. TABLE 4 Combustion Burning temperature Gas output rate Composition of generated gas Gas generating composition (° C.) (mol/100 g) (mm/sec) NO₂ NO NH₃ CO Example Fine powder of 1022 2.0982 10.59 0 22 83 135 9 melamine/BCN/BCC/Al(OH)₃/CMCNa = 15.78/69.22/5/5/5 Example Fine powder of 927 2.0508 9.03 0 20 95 130 10 melamine/BCN/BCC/Al(OH)₃/CMCNa = 15.24/64.76/10/5/5 Example Fine powder of 839 2.0036 7.57 0 16 75 125 11 melamine/BCN/BCC/Al(OH)₃/CMCNa = 14.71/60.29/15/5/5 Example Fine powder of 748 1.9583 5.70 0 13 100 80 12 melamine/BCN/BCC/Al(OH)₃/CMCNa = 14.17/55.83/20/5/5

Embodiment 13 to 17

Measurements were performed with respect to the gas generating compositions including the components shown in Table 5. The results are shown in Table 5. TABLE 5 Combustion Burning temperature Gas output rate Composition of generated gas Gas generating composition (° C.) (mol/100 g) (mm/sec) NO₂ NO NH₃ CO Example Fine powder of 1196 2.26 12.05 0 33 65 180 13 melamine/GN/BCN/BCC/CMCNa = 11.4/11.4/62.2/10/5 Example Fine powder of 1085 2.23 10.87 0 35 48 150 14 melamine/GN/BCN/BCC/CMCNa = 11.6/11.6/53.8/20/5 Example Fine powder of 1275 2.40 10.63 0 68 95 230 15 melamine/GN/BCN/BCC/CMCNa = 8/20.1/56.9/10/5 Example Fine powder of 1317 2.49 10.36 0 63 93 190 16 melamine/GN/BCN/BCC/CMCNa = 6/25.5/53.8/10/5 Example Fine powder of 1244 2.33 10.42 0 55 95 180 17 melamine/GN/BCN/BCC/CMCNa = 6/23.8/50.2/15/2

Embodiment 18 to 24

Measurements were performed with respect to the gas generating compositions including the components shown in Table 6. The results are shown in Table 6. TABLE 6 Combustion Burning temperature Gas output rate Composition of generated gas Gas generating composition (° C.) (mol/100 g) (mm/sec) NO₂ NO NH₃ CO Example Fine powder of 1382 2.59 10.25 0 19 19 170 18 melamine/GN/BCN/Al(OH)₃/CMCNa = 5/28.9/58.1/3/5 Example Fine powder of 1238 2.31 12.57 0 60 55 200 19 melamine/GN/BCN/Al(OH)₃/CMCNa = 11.7/11.7/68.6/3/5 Example Fine powder of 1164 2.30 11.57 0 30 55 170 20 melamine/GN/BCN/Al(OH)₃/CMCNa = 11.3/11.3/66.4/6/5 Example Fine powder of 1320 2.47 10.88 0 40 46 180 21 melamine/GN/BCN/Al(OH)₃/CMCNa = 8/21.2/62.8/3/5 Example Fine powder of 1267 2.45 9.83 0 48 42 180 22 melamine/GN/BCN/Al(OH)₃/CMCNa = 8/20.2/61.8/5/5 Example Fine powder of 1290 2.49 9.85 0 40 50 160 23 melamine/GN/BCN/Al(OH)₃/CMCNa = 7/22.7/60.3/5/5 Example Fine powder of 1310 2.53 9.77 0 29 80 160 24 melamine/GN/BCN/Al(OH)₃/CMCNa = 6/25.3/58.7/5/5

The invention thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A gas generating composition comprising a fuel and an oxidizing agent, the fuel being a melamine having a particle size (D₅₀), measured by a laser scattering method, of 35 μm or less.
 2. The gas generating composition according to claim 1, further comprising guanidine nitrate as the fuel.
 3. The gas generating composition according to claim 1 or 2, comprising basic copper nitrate and/or basic copper carbonate as the oxidizing agent.
 4. The gas generating composition according to claim 1 or 2, wherein basic copper nitrate and basic copper carbonate are used together as the oxidizing agent, and the content ratio thereof in this case is 1 to 100 parts by mass of the basic copper carbonate per 100 parts by mass of the basic copper nitrate.
 5. The gas generating composition according to claim 1 or 2, further comprising aluminum hydroxide. 